Can’t beat master campaign level 3-3-9 any hints?

tomoyo has an undispellable skill which raises purple attack by 100% for two rounds. So if you've got 2-3 purple heroes red starred and get a favourable tile board, you can do a decent amount of damage to the boss.

I was stuck on this level for ages because my tomoyo was only +2 and so i had to do joy coins for months to get enough frags to upgrade her because she just kept dying below red star level, i couldn't heal her fast enough even with two healers.

Don't worry about it too much, the special levels after this suck harder, especially when they heal themselves. Just blitz the levels you have beaten to get books and try the level every once in a while when you've improved your heroes.